Editing LaserDisc (section)

=== Audio ===
Sound could be stored in either analog or digital format and in a variety of [[surround sound]] formats; [[NTSC]] discs could carry a stereo analog audio track, plus a stereo [[Compact Disc|CD-quality]] [[audio data compression|uncompressed]] [[Pulse-code modulation|PCM]] [[digital audio]] track, which were ([[Eight-to-Fourteen Modulation|EFM]], [[Cross-interleaved Reed-Solomon coding|CIRC]], 16-bit and 44.1&nbsp;kHz [[sample rate]]).<ref name="dam" /> [[PAL]] discs could carry one pair of audio tracks, either analog or digital and the digital tracks on a PAL disc were 16-bit, 44.1&nbsp;kHz as on a CD; in the UK, the term "LaserVision" is used to refer to discs with analog sound, while "LaserDisc" is used for those with digital audio. The digital sound signal in both formats is [[Eight-to-Fourteen Modulation|EFM]]-encoded, as in [[CD]].<ref name="dam" />

[[Dolby Digital]] (also called AC-3) and [[Digital Theater Systems|DTS]], which are now common on DVD releases, first became available on LaserDisc, and ''[[Star Wars: Episode I – The Phantom Menace]]'' (1999) which was released on LaserDisc in Japan, was among the first home video releases ever to include 6.1 channel Dolby Digital EX Surround (along with a few other late-life releases from 1999 to 2001).<ref name="mindspring" /> Unlike DVDs, which carry Dolby Digital audio in digital form, LaserDiscs stored Dolby Digital in a [[frequency modulated]] form within a track normally used for analog audio. Extracting Dolby Digital from a LaserDisc required a player equipped with a special "AC-3 RF" output and an external [[demodulator]] in addition to an AC-3 [[Codec|decoder]]. The demodulator was necessary to convert the 2.88&nbsp;[[Megahertz|MHz]] modulated AC-3 information on the disc into a 384&nbsp;[[kbit/s]] signal that the decoder could handle.

In the mid to late 1990s, many higher-end AV receivers included the demodulator circuit specifically for the LaserDisc player's RF-modulated Dolby Digital AC-3 signal. By the late 1990s, with LaserDisc players and disc sales declining due to DVD's growing popularity, the AV receiver manufacturers removed the demodulator circuit. Although DVD players were capable of playing Dolby Digital tracks, the signals out of DVD players were not in a modulated form and were not compatible with the inputs designed for LaserDisc AC-3. Outboard demodulators were available for a period that converted the AC-3 signal to the standard Dolby Digital signal that was compatible with the standard Dolby Digital/PCM inputs on capable AV receivers. Another type marketed by Onkyo<ref>{{ cite web| title= Instructions for Onkyo ED901 decoder.|url= http://dl.owneriq.net/6/6e22327f-1a71-4992-810e-f9cacb996391.pdf }}</ref> and Marantz<ref>{{cite web |title=Marantz DP870 |url=https://audio-database.com/MARANTZ/etc/dp870-e.html |archive-url=https://web.archive.org/web/20170706181554/https://audio-database.com/MARANTZ/etc/dp870-e.html |archive-date=July 6, 2017 }}</ref> converted the RF AC-3 signal to 6-channel analog audio.

The two FM audio channels occupied the disc spectrum at 2.3 and 2.8&nbsp;MHz on NTSC formatted discs and each channel had a 100&nbsp;kHz FM deviation. The FM audio carrier frequencies were chosen to minimize their visibility in the video image, so that even with a poorly mastered disc, audio carrier beats in the video would be at least ‑35&nbsp;dB down, and thus, invisible. Due to the frequencies chosen, the 2.8&nbsp;MHz audio carrier (Right Channel) and the lower edge of the chroma signal were very close together, and if filters were not carefully set during mastering, there could be interference between the two. In addition, high audio levels combined with high chroma levels could cause mutual interference, leading to beats becoming visible in highly saturated areas of the image. To help deal with this, Pioneer decided to implement the CX Noise Reduction System on the analog tracks. By reducing the dynamic range and peak levels of the audio signals stored on the disc, filtering requirements were relaxed and visible beats greatly reduced or eliminated. The CX system gives a total NR effect of 20&nbsp;dB, but in the interest of better compatibility for non-decoded playback, Pioneer reduced this to only 14&nbsp;dB of noise reduction (the RCA CED system used the "original" 20&nbsp;dB CX system). This also relaxed calibration tolerances in players and helped reduce audible pumping if the CX decoder was not calibrated correctly.{{Citation needed|date=March 2021}}

At least where the digital audio tracks were concerned, the sound quality was unsurpassed at the time compared to consumer videotape. However, the quality of the analog soundtracks could vary greatly depending upon the disc and, sometimes, the player. Many early and lower-end LaserDisc players had poor analog audio components, and in turn, many early discs had poorly mastered analog audio tracks, making digital soundtracks in any form more desirable to serious enthusiasts. Early DiscoVision and LaserDisc titles lacked the digital audio option, but many of those movies received digital sound in later re-issues by Universal, and the quality of analog audio tracks generally improved greatly as time went on. Many discs that had originally carried old analog stereo tracks received new [[Dolby Stereo]] and [[Dolby Surround]] tracks instead often in addition to digital tracks, which helped boost sound quality. Later analog discs also applied [[CX (audio)|CX noise reduction]], which improved the signal-to-noise ratio of the audio.

DTS audio, when available on a disc, replaced the digital audio tracks; hearing DTS-encoded audio required only an [[S/PDIF]] compliant digital connection to a DTS decoder.

On a DTS disc, digital PCM audio was not available, so if a DTS decoder was also not available, the only option was to fall back to the analog Dolby Surround or stereo audio tracks. In some cases, the analog audio tracks were further made unavailable through replacement with supplementary audio such as isolated scores or audio commentary. This effectively reduced playback of a DTS disc on a non-DTS equipped system to mono audio, or in a handful of cases, no film soundtrack at all.<ref name="blam1" />

Only one 5.1 surround sound option existed on a given LaserDisc (either Dolby Digital or DTS). As such, if surround sound was desired, the disc must be matched to the capabilities of the playback equipment (LaserDisc player and receiver/decoder) by the purchaser. A fully capable LaserDisc playback system included a newer LaserDisc player that was capable of playing digital tracks; had a digital optical output for digital PCM and DTS encoded  audio; was aware of AC-3 audio tracks; and had an AC-3 coaxial output, an external or internal AC-3 RF demodulator and AC-3 decoder, and a DTS decoder. Many 1990s A/V receivers combined the AC-3 decoder and DTS decoder logic, but an integrated AC-3 demodulator was rare both in LaserDisc players and in later A/V receivers.<ref name="PrecisionLaserDisc" />

[[PAL]] LaserDiscs have a slightly longer playing time than [[NTSC]] discs, but have fewer audio options. PAL discs only have two audio tracks, consisting of either two analog-only tracks on older PAL LaserDiscs, or two digital-only tracks on newer discs. In comparison, later NTSC LaserDiscs are capable of carrying four tracks (two analog and two digital). On certain releases, one of the analog tracks is used to carry a modulated [[Dolby AC-3|AC-3]] signal for [[5.1 channel]] audio (for decoding and playback by newer LaserDisc players with an "AC-3 RF" output). Older NTSC LaserDiscs made before 1984 (such as the original DiscoVision discs) only have two analog audio tracks.